let index = 0
function promiseOut (value, time) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(value)
      index++
      if (index === 3) {
        console.log(value)
      }
    }, time)
  })
}
function promiseTimeOut () {
  promiseOut('hello', 10)
    .then(value => {
      return promiseOut(value + 'lagou', 10)
    })
    .then(value => {
      promiseOut(value + 'I ♥ U', 10)
    })
}
promiseTimeOut()
